This invention relates to a safety device for the trigger mechanism of a shot-gun of the gas-pump type. In this specification and in the claims, by the term: shot-gun of the gas-pump type is meant a shot-gun in which the re-arming mechanism may be actuated either automatically, by the so-called gas-take-off method, or manually by the so-called pump-action technique. The re-arming mechanism of a gun of the type under consideration generally includes a breechblock mounted on a carrier guided for movement towards and away from a firing chamber, a spring which maintains the breechblock in a position in which it closes the firing chamber and which resists the movement of the carrier-breechblock group away therefrom, and a piston for driving the said carrier-breechblock group against the action of the firing-chamber-closure spring. When the re-arming mechanism of the gun is actuated by the so-called gas-take-off method, the piston is subjected to the action of a portion of the discharge gas which is drawn from the gun barrel into a cylinder in which the piston is axially movable. When the re-arming mechanism of the gun is actuated manually, the piston is made rigid with a fore-end-stock-slide, slidably mounted on the gun itself. A shot-gun of the gas-pump type is further provided with a device for converting it from automatic actuation to manual actuation of the re-arming mechanism and vice versa. Such a shot-gun of the gas-pump type is described in Patent Applications Nos. 22697 B/79 and 24595 A/80 filed on the 27th Sept. 1979 and the 11th Sept. 1980 respectively in the name of the same Applicant.
When a gun is in its ready-to-fire condition, the breechblock is held in its position in which it closes the firing chamber by a positive, removable catch, called a hook in this branch of the art, while the carrier is retained in a corresponding position by a stop member generally supported by the trigger mechanism housing of the gun, More particularly, the said stop member is constituted by a lever which is fixed at one end to the trigger mechanism housing and the other end of which bears against the rear wall of the carrier. Such a stop member must be of the escape type, that is to say, it must be displaceable into a non-operative position to allow the carrier to be displaced freely in the direction of opening of the firing chamber when it is required to re-arm the gun after firing. To this end, the cited stop member is connected to the hammer of the gun and follows its anguler displacement. At the moment of firing, as the hammer is angularly displaced to strike the firing pin, the cited stop member is angularly displaced about its respective pivot point so that its free end, which previously bore against the carrier, is displaced into a non-operative position, spaced from the said carrier or at least out of the path of movement thereof. From careful observation of the movement of the hammer towards the firing pin it could be seen that, in the act of striking the firing pin, the hammer rebounded before resting finally on the firing pin itself. This rebound, although rapid and limited in size, always causes an equivalent angular displacement of the cited stop member. In essence, at each firing, the cited stop member, before finally taking up its position in which it is spaced from the path of the carrier, undergoes a very rapid "return" angular displacement, which displacement, in the following description, will be called: rebound-effect displacement.
When the re-arming mechanism of a gas-pump shot-gun is actuated manually (pump action) the said rebound-effect displacement of the cited stop member is of no consequence since, because of the rapidity with which it occurs, the said stop member is safely in the non-operative position spaced from the path of the carrier at the moment at which the carrier is displaced (manually) in the direction of opening of the firing chamber.
However, when the re-arming mechanism is actuated automatically by the discharge gases drawn from the gun barrel, the displacement of the breechblock and its carrier in opening the firing chamber is so rapid and so violent that the carrier certainly strikes the free end of the lever-stop member while it is still effecting the said rebound-effect displacement. As a result, the lever-stop member and the trigger mechanism associated therewith may break.